For the past five years, with varying regularity, three or four protesters have turned up at the side of a busy road in Brighton. They hoist placards bearing graphic images of aborted foetuses alongside the redbrick walls of Wistons clinic and accost every woman going through the gates, pushing pamphlets into their hands and urging them to "look into the face" of their unborn child.

The leaflets bear more bloody images alongside dubious medical claims and stories including one of how a 12-year-old incest victim found her life radically improved when she kept her baby.

The demonstrations, by two Christian groups with links to American anti-abortion campaigns, have been the subject of a petition against their tactics, signed by two of the city's MPs and cross-party councillors who have been inundated with complaints. Police arrested two protesters who were last month found not guilty of public order offences.

In the UK such hardline protests have generally been small, but this weekend's return to the abortion limit debate by three senior cabinet ministers, and now the prime minister, has reopened the deeply impassioned debate which many had thought was long settled. Many believe it will encourage further aggressive tactics against women, some of whom may be particularly vulnerable, seeking legal medical treatment.

It began with Maria Miller, the minister for women, saying she would like a 20-week limit instead of the current 24. She said she wanted to protect women from the trauma of later abortions. Yesterday morning home secretary Theresa May said she, too, favoured 20 weeks and by the afternoon David Cameron had backed a reduction in the present limit. All stressed they were expressing personal opinions and there was no government policy to change legislation.

But it was Jeremy Hunt, as health secretary, who in an interview with the Times said: "Everyone looks at the evidence and comes to a view about when they think that moment is, and my view is that 12 weeks is the right point for it. It is just my view about that incredibly difficult question about the moment that we should deem life to start." He added: "I don't think the reason I have that view is for religious reasons."

Those comments incensed those under the remit of his own department who pointed out furiously that, even aside from the issue of a woman's right to choose, by 12 weeks many of the congenital abnormalities or other defects in a foetus that might lead to a medical abortion were not yet detectable. "The science doesn't back him, no matter what he might be implying," said Clare Murphy, spokeswoman of the British Pregnancy Advisory Service (BPAS).

Writing in the Observer, Lord Steel, the architect of the 1967 Abortion Act, which allowed access to safe and legal abortion, said the clock had been "turned back" for women.

Abortion statistics have remained mostly static – last year 190,000 abortions took place in England and Wales in 2011, a figure that has changed little in a decade. The vast majority took place at less than 10 weeks, with one in 10 taking place at over 13 weeks.

Dr Kate Guthrie, spokesperson for the Royal College of Obstetricians and Gynaecologists, said the comments by Hunt "politicise the debate around the abortion time limit and do not put women at the centre of their care".

She questioned the basis for Hunt's reference to making his decision after looking at evidence. "What evidence is he thinking of? I can't think of anything. Reducing the time limit to 12 weeks would severely limit women's choice at an extremely difficult time in their life." She added: "If the intention is to reduce the abortion rate, then health services should invest in the provision of comprehensive contraceptive services that improve access and provide women with a range of options."

She said doctors reported that there were many reasons why some women had abortions after 12 weeks of pregnancy. These include an unplanned or unwanted pregnancy that was only picked up at a later gestation, late referral to abortion services, or a scan showing foetal abnormality. Some medical conditions are only picked up later in pregnancy while there are also social reasons that impact on a woman's decision, including changes to her personal or financial circumstances.

Campaigners say around half of all women who have abortions are already mothers, and 49% are in relationships. "So they really are making a decision not just for themselves but also for their families," said Murphy. The British Pregnancy Advisory Service carries out the majority of the post-20-week abortions in England and Wales.

"I don't use the word vulnerable lightly but they are often at their most vulnerable. To hear that the health secretary and the minister for women feel at liberty to pick on this group of women is appalling.

"It is appropriate for them to have their own personal convictions, but it is not appropriate for them to misuse science to bolster those convictions. They may have their moral qualms but they are not entitled to transpose those moral qualms on to scientists and on to women."

Diane Abbott, shadow health minister, said Hunt was using abortion as an issue to win support within the Tory party. She said it was an ideological attack on science and that it was "pretty shocking that leading Tory politicians are lining up to attack women's reproductive rights on the basis of no support in the medical community.

"There is no evidence to support a reduction in the abortion time limit and this view is supported across the medical profession. Late abortion only affects a small number of women, who are often in extremely challenging circumstances."

And indeed the row immediately galvanised calls for an official debate. Tory MP Mark Pritchard, vice-chairman of the parliamentary pro-life group, said that it was time for an "up-to-date" national discussion.

"The law currently lags behind recent scientific breakthroughs, where the survivability of young babies has increased greatly. It is time for the government to make time for a full debate on the issue. It is a tragic irony that at one end of a hospital taxpayers are paying for the termination of babies, whilst at the other end of the same hospital, taxpayers are paying to create babies through IVF."

Hunt's comments, on the eve of the Conservative party conference in Birmingham, were also welcomed by Tory backbencher Daniel Kawczynski who said there were MPs of all parties who backed a change in the law.

"The health secretary coming out in favour of reigniting this debate will galvanise the caucus that exists in parliament. There will be many of us who will never stop campaigning to reduce the limit," Kawczynski said.

The Royal College of Obstetricians and Gynaecologists and the British Medical Association said there was no change in science or in the medical opinion around abortion since the previous move to reduce the limit in 2008 which was defeated in parliament.

Around 1% of babies who are born at 22 weeks survive, although not without disability or serious health issues, which is thought to be why some feel unsettled by the present limit.

Professor Wendy Savage, a gynaecologist and campaigner, has defended the "very small" number of abortions that take place over 20 weeks and said a considerable proportion are of foetuses with a congenital abnormality, some of which will not be picked up until a late stage in the pregnancy. "I think the majority of the population think that if somebody has got a foetus that, if born, will have a severe disability, they should have the right to choose whether or not to continue with that pregnancy," she said.

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